Production of epitaxial films



United States Patent 3,364,084 PRQDUQTKGN 0F EPITAXIAL FILMS Robert A.Ruehrweiu, Dayton, Ohio, assiguor to Monsanto Company, St. Louis, Mo., acorporation of Delaware No Drawing. Continuation-impart of applicationSer. No. 821,101, June 18, 1959. This application May 29, 1961, Ser. No.129,919

14 Claims. (Cl. 148-475) This application is a continuation-in-part ofcopending US. application Ser. No. 821,101, filed June 18, 1959.

The present invention relates to a method for the production ofepitaxial films of large single crystals of inor ganic compounds.Epitaxial films which may be prepared in accordance with the inventiondescribed herein are prepared from volatile compounds of elements ofGroup III-B of the Periodic System having atomic weights of from to 119with volatile compounds of elements of Group V-B having atomic weightsof from 12 to 133. Typical compounds within this group include thebinary compounds boron phosphide, gallium arsenide, indium arsenide,gallium phosphide and indium phosphide. As examples of ternarycompositions within the defined group are those having the formulae GaAsP and InAs P x having a numerical value greater than zero and less than1.

It is an object of this invention to provide a new and economical methodfor the production of the above described class of compounds which arecharacterized as having a crystalline structure and existing aswell-defined single crystals.

A still further object of this invention is formation and deposition ofepitaxial films of the above-described materials upon substrates of thesame or different materials.

The III-B and V-B compounds of this invention are of unusual purity andhave the necessary electrical properties for use as semiconductorcomponents and are prepared by the reaction of a gaseous III-B compound,such as boron halide and a gaseous V-B compound, such as phosphorushalide in the presence of hydrogen. Examples of boron compounds whichare gaseous under the present reaction conditions include the boronhalides, e.g., boron trichloride, boron tribromide, and boron triiodide;and also alkyl boron compounds such as trimethyl boron, triethyl boron,tripropyl boron, triiso-propyl boron, and tri tert-butyl boron, as wellas alkylated boranes, such as ethyl alkylated pentaborane, and ethylalkylated decaborane having variable degrees of alkylation; and boronhydrides including diborane, pentaborane and decaborane. Other GroupIIIB starting materials which are employed in the present inventioninclude the corresponding halides and akyl compounds of aluminum,gallium and indium. Such metals are preferably employed as the halides,for example, the chlorides, bromides and iodides, although the variousalkyl and halo-alkyl derivatives may similarly be used, e.g., trimethylgallium, trimethyl aluminum, trimethyl indium, triethyl gallium, methylgallium dichlo ride, triethyl aluminum and triisobutyl aluminum. TheGroup V-B compounds which are of particular utility include the halides,hydrides and alkyl derivatives of aresnic and phosphorous. The chloridesare preferred as the source material for the Group V-B componentsemployed in the present method. The phosphorus halides which arecontemplated include phosphorus trichloride, phosphorus tribromide andphosphorus triiodide, phosphorus penta chloride and phosphoruspentabromide.

In conducting the vapor phase reaction between the Group III-B and theGroup V-B component for the production of a crystalline solid III-B, V-Bcompound, it is essential that gaseous hydrogen be present in thesystem, and that oxidizing gases be excluded. However, when the GroupIII-B and/or V-B hydrides are used it is un necessary to use molecularhydrogen, but it may be used as a carrier. The mole fraction of theill-B component in the gas phase (calculated as the mole fraction of the5 monatomic form of the III-B compound) preferably is from 0.01 to 0.15,while the mole fraction of the V-B component is from 0.05 to 0.50 (alsocalculated with respect to the monatomic form of the V-B compound). Themole fraction of the hydrogen may vary in the range of from 0.35 to0.94. It should be recognized that this repre sentation of partialpressure imposes no limitation upon the total pressure in the systemwhich may vary in the range of from 0.1 microns to several atmospheres,for example, 7500 mm. Hg.

The mole fraction of the Group VB starting material such as halide, forexample, phosphorus trichloride, is preferably at least equivalent to,and still more preferably greater than the mole fraction of the GroupIIIB halide, for example, gallium trichloride, or other Group IIIBcompound which is employed. A preferred embodiment is the use of a molefraction for the Group V-B compound which is at least twice that of theGroup III-B compound. The mole fraction of hydrogen should then be atleast twice that of the combined mole fraction of the Group III andGroup V halides.

The temperature used in carrying out the reaction between the abovedescribed III-B compound and the V-B compound in the presence ofhydrogen will generally be above about 400 C. to as much as 1500' C., apreferred operating range being from 600 C. to 1300 C. Still morepreferred ranges of temperatures for making individual productsconstituting species within the generic temperature range are:

"C BP 700l200 InP 500l000 GaP 700-1200 GaAs 600-1200 InAs 500-900 AlP500l000 AlAs 7001200 InSb 400-500 GaSb 500-650 AlSb 700-1000 BN 800-1200AlN 6001200 The only temperature requirements are that the temperatureswithin the III-B reservoir and inthe tube containing the V-B compound bemaintained above the dew points of the vaporized components therein. Forthe III-B compound this is usually within the. range of from -1000 C.and for the VB compound, from to 400 C. The time required for thereaction is dependent upon the temperature and the degree of mixing andreacting. The III-B and V-B gaseous components may be introducedindividually through nozzles, or may be premixed as desired.

The apparatus employed in carrying out the process of the presentinvention may be any of a number of types. The simplest type constitutesa closed tube of a refractory material such as glass, quartz or aceramic tube such as mullite into which the crude reactant materials areintroduced together with the hydrogen vapor. The tube is then sealed oiland subjected to temperatures within the range of from 400 to 1500 C.for a period of from less than one minute to one hour or more, until thereaction is complete.

The contacting and vapor phase precipitation may be carried out in aclosed system which is completely sealed off after the hydrogen isintroduced with the IIIB compound and the V-B compound, or by use of acontinuous 2; gas flow system. The pressure which is obtained in thesingle-vessel, closed system corresponds to the pressure exerted by theadded hydrogen vapor at the operating temperature. The pressure in thesystem may be varied over a considerable range such as from 0.1 micronto atmospheres, a preferred range being from 0.5 to 1.0 atmosphere.

On a larger scale, the present process is operated as a continuous flowsystem. This may constitute a simple reaction tube in which the seedcrystal is located and in which the hydrogen gas is then passed to flushoxygen from the system. Into this tube are passed the III-B and V-Breactants carried by hydrogen along the same or one or more additionalconduits. The III-V compound formed in the reaction tube deposits as anepitaxial layer on the seed crystal. Various other modificationsincluding horizontal and vertical tubes are also contemplated, andrecycle systems in which the exit gas after precipitation of the singlecrystal product is returned to the system is also desirable,particularly in larger scale installations.

An advantage of the present method for the production of epitaxial filmsof III-B, V-B compounds by the reaction in the vapor phase of a GroupIII-B compound and a Group V-B compound, preferably the halides, in thepresence of hydrogen is the ease of obtaining high purity products. Incontrast to this method, the conventional method for the preparation ofIII-V compounds beginning with the respective elements from the GroupIII and Group V series requires a difiicult purification technique forthe metals. The conventional purification procedures are not aseffective when dealing with the metals in contrast to the compoundsemployed in the present invention. For example, distillation,recrystallization and other conventional purification methods arereadily applicable to the starting compounds employed in the presentprocess. Furthermore, the high-temperature vapor-phase reaction employedin the present method inherently introduces another factor favoring theproduction of pure materials, since the vaporization and decompositionof the respective Group III and Group V compounds, e.-g., the halides,results in a further rejection of impurities. The desired reaction forthe production of the IIIB, VB compound occurs between the Group III-Bcompound, the Group V-B compound, and hydro gen to yield the III-Vcompound. As a result, it is found that unusually pure materials whichare of utility in various electrical and electronic applications such asin the manufacture of semiconductors are readily obtained.

The most important aspect of this invention is the provision of a meansof preparing and depositing epitaxial films of the purified singlecrystal material onto various substrates. These deposited films permitthe fabrication of new electronic devices discussed hereinafter. Thecharacteristic feature of epitaxial film formation is that starting witha given substrate material, e.g., gallium arsenide, having a certainlattice structure and oriented in any direction, a film, layer orovergrowth of the same or different material may be vapor-deposited uponthe substrate. The vapor deposit has an orderly atomic lattice andsettling upon the substrate assumes as a mirror-image the same latticestructure and geometric configuration of the substrate. When using acertain material, e.g., gallium arsenide, as the substrate and anothermaterial, e.g., indium phosphide as the film deposit it is necessarythat lattice distances of the deposit material closely approximate thoseof the substrate in order to obtain an epitaxial film.

A particular advantage of the present method for the production ofepitaxial films of III-B, VB compounds by the reaction in the vaporphase of a Group IIIB compound and a volatile Group V-B compound in thepresence of hydrogen is that in forming the epitaxial layer on thesubstrate, the substrate is not affected and therefore sharp changes inimpurity concentration can be formed. By this method it is possible toprepare sharp A and narrow junctions, such as p-n junctions, whichcannot be prepared by the conventional methods of diffusing andalloying.

The thickness of the epitaxial film may be controlled as desired and isdependent upon reaction conditions such as temperatures within thereactor, hydrogen flow rates and time of reaction. In general, theformation of large single crystals and thicker layers is favored byhigher temperatures as defined above, and lower hydrogen pressures andlarger flow rates.

As stated hereinbefore, the epitaxial films formed in accordance withthis invention comprise compounds formed from elements of Group Ill-B ofthe Periodic System and particularly those having atomic weights of from10 to 119 and elements selected from Group V-B having atomic weights offrom 12 to 133. Included in this group of compounds are the nitrides,phosphides, arsenides and antimonides of boron, aluminum, gallium andindium. The bismuthides and thallium compounds, while operable, are lesssuitable. In addition to the use of the above compounds by themselves,mixtures of these compounds are also contemplated as epitaxial films,e.g., aluminum nitride and indium antimonide mixed in varyingproportions when produced by the instant process produce suitablesemiconductor compositions.

Other combinations of elements within the above group which arecontemplated herein include ternary and quaternary compositions, ormixed binary crystals, such as combinations having the formulae GaAs PInAs P and GaAs (P N where x and y have a numerical value greater thanzero and less than 1.

Materials useful as substrates herein include the same materials used inthe epitaxial films as just described and, in addition, compounds ofelements of Groups II and VI II-VI compounds) and compounds of Groups Iand VII elements (I-VII compounds), and the elements silicon andgermanium are suitable substrates. Suitable dimensions of the seedcrystal are 1 mm. thick, 10 mm. wide and 1520 mm. long, although largeror smaller crystals may be used.

As will be described hereinafter, the materials used herein either asfilms or substrates or both may be used in a purified state orcontaining small amounts of foreign materials as doping agents.

The significance of structures having epitaxial films is that electronicdevices utilizing surface junctions may readily be fabricated. Devicesutilizing n-p or p-n junctions are readily fabricated by vapordepositing the host material containing the desired amount and kind ofimpurity, hence, conductivity type, upon a substrate having a differentconductivity type. In order to obtain a vapor deposit having the desiredconductivity type and resistivity, trace amounts of an impurity, e.g.,an element or compound thereof selected from Group II of the periodicsystem, e.g., beryllium, magnesium, zinc, cadmium and mercury areincorporated into the reaction components in order to produce p-typeconductivity, and tin or a tin compound such as tin tetrachloride or anelement from Group VI, e.g., sulfur, selenium and tellurium, to producen-type conductivity. These impurities are carried over with the reactantmaterials into the vapor phase and deposited in a uniform dispersion inthe epitaxial film of the formed product on the substrate. Since theproportion of dopant deposited with the III-V compound is notnecessarily equal to the proportion in the reactant gases the quantityof dopant added corresponds to the level of carrier concentrationdesired in epitaxial film to be formed.

The doping element may be introduced in any manner known in the art, forexample, by chemical combination with or physical dispersion within thereactants. Other examples include adding volatile dopant compounds suchas SnCl to the reservoir of the Group IIIB and/or V-B components, or thedopant can be added with a separate stream of hydrogen from a separatereservoir.

The substrate materials used herein may be doped by conventional meansknown to the art. For example, the doping agent may be introduced inelemental form or as a volatile compound of the dopant element duringpreparation of the substrate crystal in the same manner described abovefor doping the epitaxial film. Also, the dopant may be added to a meltof the substrate compound during crystal growth of the compound. Anothermethod of doping is by diffusing the dopant element directly into thesubstrate compound at elevated temperatures.

The quantity of dopant used will be controlled by the electricalproperties desired in the final product. Suitable amounts contemplatedherein range from 1X10 to 5X10 atoms/cc. of product.

Vapor deposits of the purified material having the same conductivitytype as the substrate may be utilized to form intrinsic pp+ or nn+regions.

Variations of the preceding techniques permit the formation of deviceshaving a plurality of layers of epitaxial films each having its ownelectrical conductivity type and resistivity as controlled by layerthickness and dopant concentration. Since the vapor deposited materialassumes the same lattice structure as the substrate whereever the twomaterials contact each other, small or large areas of the substrate maybe masked from or exposed to the depositing host material. By this meansone is able to obtain small regions of surface junctions or wide areafilms on the substrate for a diversity of electronic applications.

As mentioned above, a plurality of layers of epitaxial films may bedeposited upon the substrate material. This is accomplished, e.g., byvapor depositing consecutive layers one upon the other. For example, afirst film of one of the materials described herein, e.g., galliumarsenide is vapor deposited upon a substrate of germanium. Subsequently,a quantity of the same material with different doping agents ordifferent concentrations of the same dopant or another of the describedmaterials, e.g., indium phosphide may be Vapor deposited from startingmaterials comprising these elements with a fresh quantity of hydrogen asa second epitaxial film over the epitaxial film of gallium arsenidealready deposited on the substrate. This procedure with any desiredcombination of epitaxial and non-epitaxial layers can be repeated anynumber of times.

Alternatively, after the first layer of material is vapor deposited uponthe substrate, the substrate with this epitaxial layer is removed toanother reaction tube and a second material is then vapor deposited asbefore upon the substrate with its first epitaxial layer, therebyforming a two-layered component.

In each of these processes, the thickness of the film and the impurityconcentration are controllable to obtain a variety of electricalefit'ects required for specific purposes as discussed elsewhere herein.

Various electronic devices to which these epitaxially filmedsemiconductors are applicable include diodes, (e.g., tunnel diodes),parametric amplifiers, transistors, high frequency mesa transistors,solar cells, thermophotovoltaic cells, components in micromodulecircuits, rectifiers, thermoelectric generators, radiation detectors,optical filters, watt-meters, and other semiconductor devices.

The invention will be more fully understood with reference to thefollowing illustrative specific embodiments:

Example I This example illustrates the formation and deposition of anepitaxial film of p-type GaAs on n-type GaAs as the substrate.

A polished seed crystal of n-type GaAs weighing 2.88 g. and containing5.8 10 carriers/cc. of tellurium dispersed therein placed in a fusedsilica reaction tube located in a furnace. The GaAs seed crystal isplaced on a graphite support inside said tube. The reaction tube isheated to 1000 C. and a stream of hydrogen is directed through the tubefor 15 minutes to remove oxygen from the surface of the GaAs.

A stream of hydrogen is then directed through a reservoir of GaClmaintained at about 130 C. thus vaporizing the GaCl which is thencarried by the hydrogen through a heated tube from the reservoir to thereaction tube containing the GaAs seed crystal.

Meanwhile, separate and equal streams of hydrogen are conducted throughseparate tubes containing in one of them a reservoir of arsenictrichloride heated to about C. and in the other a body of zinc chlorideheated to about 3 60 C. From the heated tubes the arsenic tri chlorideand zinc chloride are carried by the hydrogen on through the tubes tothe reaction tube. In the system the mole fractions of the GaCl AsCl andhydrogen are 0.05, 0.15 and 0.80, respectively. The separate streams ofvaporized AsCl GaCl and Zinc chloride conjoin in the fused silicareaction tube where a reaction occurs between the arsenic and gallium inwhich a single crystal film of ptype gallium arsenide is formed on theseed crystal of H- type gallium arsenide forming thereon an epitaxiallayer which exhibits about 10 carriers (holes) per cc. The seed crystalafter 5 hours weighs 3.44 g.

X-ray diffraction patterns of the substrate crystal show that thedeposited layer is single crystal in form and oriented in the samefashion as the substrate.

Point contact rectification tests show that a p-n junction exists at theregion of the junction between the epitaxial layer and the seed crystalsubstrate.

Example 2 The same procedure outlined in Example 1 is repeated butphosphorus trichloride heated to about 60 C. is substituted for thearsenic trichloride and gallium tribromide heated to about 230 C. issubstituted for gallium trichloride. In this example, a seed crystal ofn-type Gal weighing 1.45 g. and containing about 5.5 10 carriers/cc. ofsulfur dispersed therein is used. The. partial pressures of the GaBr PCland H are 0.10, 0.20 and 0.70, respectively.

In the reaction tube, the vaporous GaBr PCI zinc dopant and hydrogenreact to form p-type GaP which precipitates from the vapor phase ontothe seed crystal of n-type Gal. The reaction is allowed to proceed for 7hours, after which the Gal is removed from the reaction tube, weighedand is found to have increased in weight by 0.01 g. The crystal uponX-ray examination is found to consist of an overgrowth of single crystalp-type GaP having the same crystal orientation as the n-type GaPsubstrate. The crystal exhibits rectification showing that a p-njunction exists at the boundary between the epitaxial overgrowth and thesubstrate.

Example 3 This example illustrates the formation of a product having ann-type InP overgrowth on a p-type GaAs substrate.

The apparatus and procedure outlined in Examples 1 and 2 are used andfollowed generally, except that the reservoir containing the III-Bcompound, i.e., indium trichloride also contains a quantity of avolatile compound to be used as the doping agent for the vapor-depositedcompound. To the indium trichloride in the reservoir is added TeCl inthe amount corresponding to 0.01% of the amount of InCl i.e., asufiicient quantity to yield 1X 10 carriers/cc. in the depositedproduct. In a second tube leading to the reaction tube is a reservoir ofphosphorus trichloride.

A seed crystal of gallium arsenide containing about 5.7 l carriers/cc.zinc dispersed therein to provide ptype conductivity, is placed in thereaction tube located in the furnace. The furnace is then heated to 800C. and a stream of hydrogen directed through the reaction tube for about20 minutes to remove any oxygen present.

The reservoir of indium chloride containing the tellurium chloride isheated to 430 C. to volatilize the components which are conducted by astream of hydrogen passing through the reservoir, to the reaction tube.Simultaneously, the second tube containing the phosphorus trichloride isheated to about 60 in the presence of a stream of hydrogen. Thevaporized phosphorus trichloride is also carried to the reaction tubewherein the indium chloride reacts with the phosphorus trichloride andhydrogen in the presence of the tellurium dopant to produce n-typeindium phosphide which deposits from the vapor phase as a uniform layerupon the seed crystal of p-type gallium arsenide.

The product, upon examination shows an epitaxial layer of single crystalindium phosphide having the same crystal orientation as the galliumarsenide substrate and exhibits rectification indicating the existenceof a p-n junction between the epitaxial layer and the substrate.

Example 4 This example illustrates the preparation of an indiumphosphide substrate having deposited thereon an epitaxial overgrowth ofaluminum antimonide.

The procedure described in the preceding example is repeated, exceptthat the seed crystal used is p-type indium phosphide containing about5.1 X 10 carriers/ cc. of cadmium dispersed therein. The reservoircontaining the III-B compound, i.e., methyl aluminum dichloride alsocontains sufficient tin chloride doping agent to dope the subsequentlyformed aluminum antimonide to a carrier concentration of about 1X10carriers/ cc. The VB compound used in this example is antimonytrichloride. The tube containing the reservoir of antimony trichlorideis heated to 200 C. while passing a stream of hydrogen therethrough,while the methyl aluminum dichloride and tin tetrachloride are heated to200 C. in a stream of hydrogen. These separate streams of hydrogencontaining the vaporized reactants are then conducted to the reactiontube which is heated to 1000 C. and contains the indium phosphide seedcrystal. Here, the vaporized reactants intermix forming aluminumantimonide containing the tin doping agent dispersed therein. Thisproduct precipitates from the vapor phase and deposits on the indiumphosphide seed crystal.

Again, X-ray difiraction patterns of the substrate crystal show that thedeposited layer is single crystal in form and oriented in the samemanner as the substrate.

Point contact rectification tests show the presence of a. p-n junctionas in preceding examples.

Example 5 This example illustrates the procedure for producing a producthaving a plurality of layers of different electrical properties.

The procedure here is similar to that followed in the preceding example,and the apparatus is the same.

The reservoir containing the IlIB compound, gallium triiodide, is heatedto 350 C. in a stream of hydrogen, While the tube containing a reservoirof arsenic triiodide is heated to about 390 C. in a stream of hydrogenand a separate tube containing ZnCl is heated to about 360 C. in astream of hydrogen. These separate streams of hydrogen containing thevaporized reactants are conducted to the reaction tube which contains aseed crystal of polished elemental germanium doped to a carrierconcentration of about 5.8 atoms/ cc. of phosphorus. In the reactiontube previously flushed with hydrogen and heated to 900 C., the galliumtriiodide reacts with the hydrogen, arsenic triiodide and zinc chloridedopant to form p-ty-pe gallium arsenide which deposits from the vaporphase onto the n-type germanium seed crystal. The reaction proceeds forabout 15 minutes, after which the flow of the separate streams ofhydrogen is discontinued temporarily. A fresh supply of arsenictriiodide doped with a trace amount of tellurium tetraiodide is added toreplace the original arsenic source.

After the fresh source of arsenic triiodide is charged to the system,the hydrogen supply is again opened to stream through the III-B compoundreservoir, again heated to 350 C. and the arsenic triiodide-telluriumtetraiodide source heated to 390 C. Again, the vaporized reactants arecarried by the hydrogen to the reaction tube heated to l000 C. In thereaction tube the gallium triiodide reacts with the doped arsenictriiodide to form n-type gallium arsenide which deposits upon the p-typegallium arsenide layer previously deposited on the n-type germanium seedcrystal.

After the reaction has proceeded to completion, the product, uponexamination is found to consist of a substrate of n-type germanium,having successive layers of ptype gallium arsenide and n-type galliumarsenide. These deposited layers exhibit the same X-ray orientationpattern as the single crystal germanium substrate indicating the sameorientation and single crystal form characteristic of epitaxial films.

The product further exhibits characteristic n-p-n junction propertiesshowing the presence of an n-p junction between the n-type galliumarsenide and the p-type gallium arsenide and a p-n junction between thelatter compound and the n-type germanium substrate. When this example isrepeated substituting silicon for germanium, substantially similarresults are obtained.

By this method any number and combination of epitaxial and non-epitaxiallayers may be deposited one upon the other.

An alternative to the foregoing procedure is to connect a fourth tubecontaining a second III-B compound reservoir and hydrogen supply to thereaction tube at a point near the junction of the tube containing thefirst III-B compound reservoir and the tube containing the V- B compoundreservoir. The fourth tube is closed off during the first phase of theprocess, i.e., while the first epitaxial layer is being formed, andthereafter, opened to the system while closing off the tube containingthe first III- B compound.

A still further modification of this invention is to use a mixture ofGroup III-B compounds in one or more reservoirs and/ or a mixture of theGroup VB compounds in another reservoir(s) and proceed in the usualmanner. An illustration of this modification is shown in the followingexample wherein an epitaxial film of a ternary composition of III-Velements is deposited on a gallium phosphide substrate.

Example 6 A polished seed crystal of p-type gallium phosphide containing55x10 carriers/ cc. of zinc dispersed therein is placed in the fusedsilica reaction tube. The tube is heated to 1000 C. and a stream ofhydrogen is directed through the tube for 15 minutes to remove anyoxygen present.

A mixture of gallium trichloride and indium trichloride is placed in thereservoir for the III-B compound reactant as described in precedingexamples, and a body of phosphorus trichloride is placed in another tubeconnected to the reaction tube. The phosphorus trichloride containsabout 0.1% of sulfur monochloride.

A stream of hydrogen is then directed through the reservoir containingthe mixture of IIIB halides and heated to about C., while a stream ofhydrogen is then passed through the phosphorus trichloride reservoir inthe other tube heated to about 60 C. The vaporized components in bothtubes are then carried by the hydrogen to the reaction tube containingthe gallium phosphide seed crystal. In the reaction tube heated to 1000C., the vaporized gallium chloride-indium chloride mixture combines andreacts with the hydrogen, vaporized phosphorus trichloride and sulfurchloride to form a mixed binary crystal of gallium indium phosphidewhich deposits from the vapor phase in single crystal form as anepitaxial film on said p-type gallium phosphide seed crystal. The p-typemixed crystal layer is shown by X-ray diffraction patterns to have thesame crystal orientation as the seed crystal, characteristic ofepitaxial layers.

Rectification tests establish the existence of a p-n junction betweenthe epitaxial layer and the substrate.

By varying the hydrogen flow rates through the respective III-B and V-Bcompound reservoirs according to the foregoing modification of thisexample, epitaxial films of ternary compositions over the whole range ofare obtained, where x has a value less than 1 and greater than zero.

In accordance with the present embodiment of this invention, epitaxialfilms of ternary compositions of III- B, V-B elements may be preparedmerely by reacting one volatile compound of Group III-B elements withtwo Group V-B compounds or vice-versa, i.e., by reacting two Group III-Bcompounds with one Group V-B compound in the presence of hydrogen. Thus,epitaxial films of these ternary compositions may be formed by reactinga sum of three Group III-B compounds and Group V-B compounds in anycombination in the presence of hydrogen.

Example 7 This example illustrates the preparation of epitaxial films ofquaternary mixed binary crystals of III-V elements.

A mixture of gallium and indium trichlorides is placed in one reservoirand a mixture of arsenic trichloride and phosphorus trichloridecontaining a small amount of tel lurium tetrachloride is placed in asecond reservoir. Both reservoirs are connected to a quartz tubecontaining a polished seed crystal of zinc-doped GaAs. (This arrangementmay be varied a number of ways, e.g., by placing each reactant inseparate reservoirs along a common conduit to the reaction tube or eachreservoir may have its own conduit to the reaction tube.)

The reservoir containing the gallium and indium trichlorides is thenheated to about 130 C. and the reservoir containing the telluriumtetrachloride-doped phosphorus trichloride-arsenic trichloride mixtureis heated to about 100 C. while hydrogen streams are directed throughboth tubes. The vaporized components in both reservoirs are thenconducted by the hydrogen through quartz tubes to the reaction tubewhich is heated to about 1100-1150 C. The separate streams of hydrogencarrying the reactants converge in the reaction tube where the galliumand indium trichlorides are reacted with the phosphorus and arsenictrichlorides containing tellurium tetrachloride for about 1 hour in thepresence of hydrogen to form a fourcomponent mixed binary crystal havingthe formula Ga In As P which deposits as an epitaxial film on the GaAsseed crystal.

This product having a gallium arsenide substrate of p-type conductivityand an epitaxial film of n-type conductivity exhibits rectificationsuitable for use in semiconductor devices.

Similarly, other four-component mixed binary crystals of III-V compoundsmay be deposited as epitaxial films merely by reacting in the presenceof hydrogen at least one volatile compound of Group III-B elements withat least one volatile Group V-B compound, provided that the sum of theIII-B compounds and the V-B compounds reacted equals four. That is, one,two or three Group IILB compounds may be reacted with, respectively,three, two or one Group V-B compounds in the presence of hydrogen toproduce epitaxial films of the quaternary compositions of Ill-V elementsin this embodiment of the present invention.

10 Example 8 This example illustrates the deposition of an epitaxialfilm of indium arsenide onto a substrate of a I-VII compound having thecubic zinc blende structure typified by single crystal iodide.

A polished seed crystal of single crystal copper iodide havingapproximate dimensions of 2 mm. thick, 15 mm. Wide and 20 mm. long isplaced in a fused silica reaction tube located in a furnace. Thereaction tube is heated to 550 C. and a stream of hydrogen is directedthrough the tube for 15 minutes to remove oxygen from the system.

A stream of hydrogen is then directed through a reservoir of InClcontaining about 0.000l% TeCl and maintained at about 430 C. thusvaporizing the InCl and Tech; which are then carried by the hydrogenthrough a heated tube from the reservoir to the reaction tube containingthe copper iodide seed crystal.

Meanwhile, a separate and equal stream of hydrogen is conducted througha separate tube containing a body of arsenic trichloride heated to C.From this heated tube the vaporized arsenic tricliloride is carried bythe hydrogen on through the tube to the reaction tube. In the system,the mole fractions of InCl arsenic trichloride and hydrogen are 0.05,0.15 and 0.80, respectively.

The separate streams of hydrogen from the InCl and arsenic trichlorideconjoin in the fused silica reaction tube where a reaction occursbetween the hydrogen, arsenic trichloride and indium trichloride inwhich a single crystal form of n-type indium arsenide is formed as afilm-deposit on the single crystal copper iodide substrate.

X-ray diffraction patterns of the film deposit and substrate show thatthe deposited layer is single crystal in form and has the same latticeorientation as the substrate, hence, the indium arsenide forms anepitaxial film on the single crystal copper iodide substrate.

The Hall coeflicient of the film of InAs on the copper iodide substrateis found to be 3 00* cm. coulomb, making it of utility in magnetic Halldevices. The film also exhibits photoconduction.

While the foregoing example has illustrated the use of single crystalI-Vll compounds using copper iodide as the substrate, in a similarmanner the fluorides, chlorides, bromides and iodides of copper, silverand gold are like wise used as substrates for epitaxial overgrowths ofIII-V compounds. Similarly, single crystal I-VII compounds having thecubic sodium chloride type structure may be used as substrate forepitaxial growth of III-V compounds when the I-VII crystal face uponwhich growth is to occur is the (III) crystallographic face. In thismanner, the fluorides, chlorides, bromides and iodides of sodium,lithium, potassium, rubidium and cesium are used as substrates.Preferred I-VII compounds include copper fluoride, copper chloride,copper bromide, copper iodide and silver iodide.

Example 9 This example illustrates the deposition of an epitaxial filmof gallium arsenide onto a substrate of a IIVI compound having the cubiczinc blende structure typified by single crystal zinc selenide.

A polished seed crystal of single crystal n-type zinc selenide (dopedwith boron) having approximate dimensions of 2 mm. thick, 100* mm. wideand I5 mm. long is placed in a fused silica reaction tube located in afurnace. The reaction tube is heated to 850 C. and a stream of hydrogenis directed through the tube for 15 minutes to remove oxygen therefrom.

A stream of hydrogen is then directed through a reservoir of galliumchloride maintained at C. thus vaporizing the gallium chloride which isthen carried by the hydrogen through a heated tube from the reservoir tothe reaction tube containing the zinc selenide seed crystal.

Meanwhile, separate and equal streams of hydrogen are conducted throughtwo separate tubes containing, respectively, a body of arsenictrichloride heated to 100 1 l C. and a body of zinc chloride heated to360 C. From these heated tubes the arsenic trichloride and zinc chlorideare carried by the hydrogen on through the tubes to the reaction tube.In the system, the mole fractions of GaCl AsCl and hydrogen are 0.05,0.15 and 0.80, respectively.

The separate streams of hydrogen carrying the GaCl AsCl and ZnCl conjoinin the fused silica reaction tube where a reaction occurs between thehydrogen, arsenic trichloride and gallium trichloride in which a singlecrystal form of p-type gallium arsenide is formed as a fi'mdeposit onthe single crystal zinc selenide substrate.

X-ray diffraction patterns of the film deposit and substrate show thatthe deposited layer is single crystal in form and has the same latticeorientation as the substrate, hence, the gallium arsenide forms anepitaxial film on the single crystal zinc selenide substrate. Thecrystal exhibits rectification showing that a p-n junction exists at theboundary between the epitaxial overgrowth and the substrate.

While the foregoing example has illustrated the use of single crystalIIVI compounds using Zinc selenide as the substrate, in a similar mannerthe sulfides, selenides and tellurides of beryllium, zinc, cadmium, andmercury are likewise used as substrates for epitaxial overgrowths ofIIIV compounds. Similarly, single crystal IIVI compounds having thecubic sodium chloride type structure may be used as substrates forepitaxial growth of the III-V compounds when the II-VI crystal face uponwhich growth is to occur is the (III) crystallographic face. In thismanner the oxides, sulfides, selenides and tellurides of magnesium,calcium, strontium and barium, as well as cadmium oxide, are used assubstrates. Preferred II-VI compounds include zinc sulfide, zincselenide, zinc telluride, cadmium sulfide, cadmium selenide, cadmiumtelluride, mercury sulfide, mercury selenide, mercury telluride,beryllium sulfide, beryllium selenide and beryllium telluride.

It will be seen that the products obtained according to the presentinvention have a variety of applications. For example, in electronicdevices where it is desirable to have a substantially inertnon-conducting base for III-V semiconductors, the product described inExample 8 is highly suitable. Where it is desired to obtainsemiconductor components having semiconducting properties in the basematerial as well as in the epitaxial film, those products described inExamples 1-7 and Example 9 above are of particular value.

Electronic devices may also be fabricated wherein a semiconductingcomponent comprising an epitaxial film of III-V compositions isdeposited on substrates of metallic conductors having cubic crystalstructure, such as gold, silver, calcium, cerium, cobalt, iron, iridium,lanthanum, nickel, palladium, platinum, rhodium, strontium, thorium andcopper, and alloys such as AlZn, SbCoMn, BTi and Cr Ti.

Various other modifications of the instant invention will be apparent tothose skilled in the art without departing from the spirit and scopethereof.

I claim:

1. Process for the production and deposition of epitaxial films ofcompounds of Group IIIB elements having atomic weights of from 10 to 119and elements selected from Group VB having atomic weights of from 12 to133 and mixtures thereof onto a substrate material crystallographicallycompatible with said films and selected from the group consisting ofIII-V compounds, I-VII compounds, II-VII compounds, germanium andsilicon, which comprises combining in the vapor phase at least onevolatile compound of Group III-B elements together with at least onevolatile compound of Group VB elements in the presence of hydrogen, andcontacting the resulting reaction mixture with said substrate whereby apurified single crystal form of at least one III-V com- 1?; pound isdeposited from said reaction mixture as an epitaxial film on saidsubstrate.

2. Process for the production and deposition of epitaxial films ofcompounds of Group III-B elements having atomic weights of from 10 to119 and elements selected from Group VB having atomic weights of from 12to 133 and mixtures thereof onto a substrate material crystallographically compatible with said films and selected from the groupconsisting of III-V compounds, I-VII compounds, II-VI compounds,germanium and silicon, which comprises combining in the vapor phase attemperatures within the range of from 400 to 1500 C. at least onevolatile compound of Group III-B elements selected from the classconsisting of halides, hydrides, and alkyl derivatives together with atleast one volatile compound of Group VB elements selected from the groupconsisting of halides, hydrides and alkyl derivatives in the presenceor" hydrogen and contacting the resulting reaction mixture with saidsubstrate whereby a purified single crystal form of at least one III-Vcompound is deposited as an epitaxial film on said substrate.

3. Process according to claim 2 wherein said Group III-B compound isgallium trichloride, said Group VB compound is arsenic trichloride andsaid III-V compound deposited as an epitaxial film is gallium arsenide.

4. Process according to claim 2 wherein said Group IIIB compound istriethyl gallium, said Group VB compound is phosphorus triiodide andsaid III-V compound is gallium phosphide.

5. Process for the production and deposition of epitaxial films ofcompounds of Group III-B elements having atomic weights of from 10 to 119 and elements selected from Group VB having atomic weights of from 12to 133 and mixtures thereof, said compounds having p-type conductivityby incorporation therein of a small amount of a doping agent selectedfrom Group II of the periodic system, onto a substrate materialcrystallographically compatible with said films and selected from thegroup consisting of III-V compounds, I-VII compounds, II-VI compounds,germanium and silicon, said substrate having n-type conductivity byincorporation therein of a small amount of a doping agent selected fromGroup VI of the periodic system, which comprises combining in the vaporphase at least one volatile compound of Group III-B elements togetherwith at least one volatile compound of Group VB elements in the presenceof hydrogen, and contacting the resulting reaction mixture with saidsubstrate whereby a purified single crystal form of at least one III-Vcompound is deposited from said reaction mixture as an epitaxial film onsaid substrate forming a p-n junction therewith.

6. Process for the production and deposition of an epitaxial film ofp-type gallium arsenide onto a substrate of n-type gallium arsenide,which comprises combining in the vapor phase gallium trichloride witharsenic trichloride in the presence of hydrogen and a doping agentselected from Group II, and contacting the resulting reaction mixturewith said substrate whereby a purified single crystal form of galliumarsenide containing a small amount of said doping agent dispersedtherein is deposited from said reaction mixture as an epitaxial filmhaving p-type conductivity on said substrate having n-type conductivitythereby forming a p-n junction.

7. Process of the production and deposition of epitaxial films ofcompounds of Group III-B elements having atomic weights of from 10 to119 and elements selected from Group VB having atomic weights of from 12to 133 and mixtures thereof, said compounds having n-type conductivityby incorporation therein of a small amount of a doping agent selectedfrom Group VI of the periodic system, onto a substrate materialcrystallographically compatible with said films and selected from thegroup consisting of III-V compounds, I-VII compounds, II-VI compounds,germanium and silicon, said substrate having p-type conductivity byincorporation therein of a small amount of a doping agent selected fromGroup II of the perodic system, which comprises combining in the vaporphase at least one volatile compound of Group IIIB elements togetherwith at least one volatile compound of Group V-B elements in thepresence of hydrogen, and contacting the resulting reaction mixture withsaid substrate whereby a purified single crystal form of at least oneIII-V compound is deposited from said reaction mixture as an epitaxialfilm on said substrate forming a p-n junction therewith.

8. Process for the production and deposition of an epitaxial film ofn-type gallium phosphide onto a substrate of p-type gallium phosphide,which comprises combining in the vapor phase gallium tribromide withphosphorus triiodide in the presence of hydrogen and a doping agentselected from Group VI, and contacting the resulting reaction mixturewith said substrate, whereby a purified single crystal form of galliumphosphide containing a small amount of said doping agent dispersedtherein is deposited from said reaction mixture as an epitaxial filmhaving n-type conductivity on said substrate having p-type conductivity,thereby forming an n-p junction.

9. Process for the production and deposition of epitaxial films of mixedbinary crystals comprising elements selected from Group III-B havingatomic weights of from to 119 and elements selected from Group V-Bhaving atomic weights of from 12 to 133 onto a substrate materialcrystallographically compatible with said films and selected from theclass consisting of III-V compounds, I-VII compounds, II-VI compounds,germanium and silicon, which comprises reacting in the vapor phase atleast one volatile compound of Group III-B elements together with atleast one volatile Group V-B compound provided that the sum of the GroupIIIB compounds and Group V-B compounds reacted is greater than two, inthe presence of hydrogen and contacting the resulting reaction mixturewith said substrate whereby a purified single crystal form of mixedbinary crystals is deposited from said reaction mixture as an epitaxialfilm on said substrate.

10. Process for the production and deposition of epitaxial films ofthree-component mixed binary crystals comprising elements selected fromGroup III-B having atomic weights of from 10 to 119 and elementsselected from Group V-B having atomic weights of from 12 to 133 onto asubstrate material crystallographically compatible with said films andselected from the class consisting of III-V compounds, I-VII compounds,II-VI compounds, germanium and silicon, which comprises reacting in thevapor phase at least one volatile compound of Group III-B elementstogether with at least one volatile Group V-B compound, provided thatthe sum of the Group III-B compounds and Group V-B compounds reactedequals three, in the presence of hydrogen, and contacting the resultingreaction mixture with said substrate material, whereby a purified singlecrystal form of threecomponent mixed binary crystals is deposited fromsaid reaction mixture as an epitaxial film on said substrate.

11. Process according to claim 10 whereby said volatile III-B compoundis gallium trichloride and said Group V-B compounds are arsenictrichloride and phosphorus trichloride.

12. Process according to claim 11 wherein said mixed binary crystal isgallium arsenide phosphide having the formula GaAs,;l where x has avalue greater than zero and less than one, and said substrate is galliumarsenide.

13. Process for the production and deposition of epitaxial films offour-component mixed binary crystals comprising elements selected fromGroup III-B having atomic weights of from 10 to 119 and elementsselected from Group VB having atomic Weights of from 12 to 133, onto asubstrate material crystallographically compatible with said films andselected from the class consisting of III-V compounds, I-VII compounds,II-VI compounds, germanium and silicon, which comprises reacting in thevapor phase at least one volatile compound of Group III-B elementstogether with at least one volatile Group V-B compound, provided thatthe sum of the Group IIIB compounds and Group VB compounds reactedequals four, in the presence of hydrogen, and contacting the resultingreaction mixture with said substrate material, whereby a purified singlecrystal form of fourcomponent mixed binary crystals is deposited fromsaid reaction mixture as an epitaxial film on said substrate.

14. Process for the production and deposition of a plurality ofepitaxial layers of compounds selected from the group consisting ofcompounds of Group III-B elements having atomic weights of from 10 to119 and Group V-B elements having atomic Weights of from 12 to 133, andmixtures thereof, onto a substrate material crystallographicallycompatible with said films and selected from the group consisting ofIIIV compounds, I-VII compounds, II-VI compounds, germanium and silicon,which comprises as a first step reacting in the vapor phase at least onevolatile compound of Group III-B elements together with at least onevolatile Group V-B compound in the presence of hydrogen, and contactingsaid resulting reaction mixture with said substrate whereby a singlecrystal form of at least one III-V compound is deposited from said vaporphase as a first epitaxial layer on said substrate, repeating thisprocedure as many times as the number of layers desired, but providingmodified electrical properties in each succeeding layer by inclusiontherein of small amounts of doping agents.

References Cited UNITED STATES PATENTS vol. 3, No. 8, January 1961, page33.

DAVID L. RECK, Primary Examiner. RAY K. WINDHAM, HYLAND BIZO T,Examiners. M. A. CIOMEK, N. F. MARKVA, Assistant Examiners.

1. PROCESS FOR THE PRODUCTION AND DEPOSITION OF EPITAXIAL FILMS OFCOMPOUNDS OF GROUP III-B ELEMENTS HAVING ATOMIC WEIGHTS OF FROM 10 TO119 AND ELEMENTS SELECTED FROM GROUP V-B HAVING ATOMIC WEIGHTS OF FROM12 TO 133 AND MIXTURES THEREOF ONTO A SUBSTRATE MATERIALCRYSTALLOGRAPHICALLY COMPATIBLE WITH SAID FILMS AND SELECTED FROM THEGROUP CONSISTING OF III-V COMPOUNDS, I-VII COMPOUNDS, II-VII COMPOUNDS,GERMANIUM AND SILICON, WHICH COMPRISES COMBINING IN THE VAPOR PHASE ATLEAST ONE VOLATILE COMPOUND OF GROUP III-B ELEMENTS TOGETHER WITH ATLEAST ONE VOLATILE COMPOUND OF GROUP V-B ELEMENTS IN THE PRESENCE OFHYDROGEN, AND CONTACTING THE RESULTING REACTION MIXTURE WITH SAIDSUBSTRATE WHEREBY A PURIFIED SINGLE CRYSTAL FORM OF AT LEAST ONE III-VCOMPOUND IS DEPOSITED FROM SAID REACTION MIXTURE AS AN EPITAXIAL FILM ONSAID SUBSTRATE.